Water quality associated with survival of submersed aquatic vegetation along an estuarine gradient

The decline of submersed aquatic vegetation (SAV) in tributaries of the Chesapeake Bay has been associated with increasing anthropogenic inputs, and restoration of the bay remains a major goal of the present multi-state “Bay Cleanup” effort. In order to determine SAV response to water quality, we quantified the water column parameters associated with success of transplants and natural regrowth over a three-year period along an estuarine gradient in the Choptank River, a major tributary on the eastern shore of Chesapeake Bay. The improvement in water quality due to low precipitation and low nonpoint source loadings during 1985–1988 provided a natural experiment in which SAV was able to persist upstream where it had not been for almost a decade. Mean water quality parameters were examined during the growing season (May–October) at 14 sites spanning the estuarine gradient and arrayed to show correspondence with the occurrence of SAV. Regrowth of SAV in the Choptank is associated with mean dissolved inorganic nitrogen <10 μM; mean dissolved phosphate <0.35 μM; mean suspended sediment <20 mg l^?1; mean chlorophylla in the water column <15 μg l^?1; and mean light attenuation coefficient (Kd) <2 m^?1. These values correspond well with those derived in other parts of the Chesapeake, particularly in the lower bay, and may provide managers with values that can be used as target concentrations for nutrient reduction strategies where SAV is an issue.     

Distribution and community structure of estuarine copepods

Distribution, abundance, and community structure were studied over a 30 month period in the planktonic copepod community of the estuaries near Beaufort, North Carolina. Many of the copepod species showed a demersal distribution during the day and entered the surface waters at night. Several species were largely confined to vegetated littoral areas during the day. The copepod community showed consistent trends of seasonal abundance and succession of dominant species which differed greatly from those found by previous workers, whose methods were inadequate to sample quantitatively the small, demersal copepods which dominated the community. Copepod abundances were higher than found in previous studies and were correlated with water temperature. Species composition changed from a winter community dominated byCentropages spp., to a spring community dominated byAcartia tonsa, to a summer community jointly dominated byParacalanus crassirostris andOithona spp. Copepods were much more important grazers in these estuaries than previous studies had concluded.     

Effect of estuarine flow on ocean circulation using a coupled coastal-bay estuarine model: an application to the 1999 Orissa cyclone

A coupled coastal-bay estuarine numerical model is described and applied to investigate the combination of wind-estuarine driven circulation off the Orissa coast. The model is based on coupling of a 2-dimensional estuarine model with a 3-dimensional coastal-bay model. The models are linked through the elevation at the interface. Using the coupled model, the numerical experiments are carried out to elicit the dynamical linking between the estuarine outflow and the coastal ocean to simulate the ensuing adjoining coastal circulation. During the southwest monsoon, it is noticed that the estuarine discharge from the northern head-bay river system and the river systems that join the Bay of Bengal along the Orissa coast would sufficiently modify the coastal circulation along the coast. Numerical experiments are also carried for the model simulation of surges generated by the 1999 Orissa cyclone. It is shown that the estuarine system would influence significantly on surge development and associated inundation through the rivers.     

Temporal responses of the macrophyte,Potamogeton perfoliatus L., and its associated autotrophic community to atrazine exposure in estuarine microcosms

Estuaries and Coasts - Effects of the herbicide, atrazine, on the submersed vascular plant,Potamogeton perfoliatus, were monitored for 4 wk in 700 l microcosms containing water, sediments and...     

The relationships among man’s activities in watersheds and estuaries: A model of runoff effects on patterns of estuarine community metabolism

Activities of man in rivers and their watersheds have altered enormously the timing, magnitude, and nature of inputs of materials to estuaries. Despite an awareness of large-scale, long-term changes in river-estuarine watersheds, we do not fully understand the consequences to estuarine ecosystems of these activities. Deforestation, urbanization, and agriculturalization have changed the timing and nature of material inputs to estuaries. Conversion of land from forest to almost any other land use promotes overland flow of storm runoff; increases the timing, rate and magnitude of runoff; and increases sediment, organic matter, and inorganic nutrient export. It has been estimated that total organic carbon levels in rivers have increased by a factor of 3–5 over natural levels. Man’s activities have also changed the magnitude of particulate organic carbon relative to dissolved organic carbon export and the lability of the organic matter. Historically, rivers and streams had different features than they do today. Two of man’s activities that have had pronounced effects on the timing and quality of river water are channelization and damming. Agricultural drainage systems, channelized and deepened streams, and leveeing and prevention of overbank flooding have had the combined effect of increasing the amplitude and rate of storm runoff, increasing sediment load, increasing nutrient delivery downstream, and decreasing riparian wetland productivity. Dams on the other hand have altered natural discharge patterns and altered the downstream transfer of sediments, organic matter, and nutrients. Patterns of estuarine community metabolism are sensitive to variations, in the timing, magnitude, and quality of material inputs from watersheds. The autotrophic-heterotrophic nature of an estuary is determined by three primary factors: the ratio of inorganic to organic matter inputs, water residence time, and the overall lability of allochthonous organic matter inputs. A simulation model is used to explore the effects of man’s activities in watersheds on the spatial patterns of production and respiration in a generalized estuarine system. Examined are the effects of variations in the ratios of inorganic and organic nitrogen loading, the residence time of water in the estuary, the degradability of allochthonous organic matter, and the ratio of dissolved to particulate organic matter inputs. Simulations suggest that the autotrophic-heterotrophic balance in estuaries is more sensitive to variations in organic matter loading than inorganic nutrient loading. Water residence time and flocculation-sedimentation of organic matter are two physical factors that most effect simulated spatial patterns of metabolism in estuaries.     

页岩储层岩石物理模型及地震AVO响应模拟

通过模拟并分析各向异性页岩岩石物理模型,研究页岩中干酪根含量变化对页岩弹性各向异性的影响,其结果为应用AVO方法定量解释页岩储层厚度和干酪根含量提供依据。岩石物理模型预测了页岩速度和各向异性参数随干酪根含量的变化规律。应用传播矩阵方法计算薄层页岩的AVO响应,得到反射系数关于页岩层厚度、入射波频率、干酪根含量和入射角的函数。数值模拟结果表明:在干酪根含量不变且在同一入射角下的反射系数在频率域呈周期变化,该周期与薄层厚度成反比;对同一频率入射波和相同入射角,反射系数幅值随干酪根含量增加而变大。     

Calibration of an elasto-plastic constitutive model by a constrained optimisation procedure

The presented paper deals with a constrained optimisation technique for the calibration of elasto-plastic model parameters in a rational and objective manner. The procedure consists in finding a set of model parameters which minimise the difference between the experimental data and the numerical simulations defined by an objective function. For this purpose, an optimisation routine, termed ParaID, has been developed which combines the quasi-Newton and stochastic methods. The optimisation technique was employed to calibrate a multi-mechanism elasto-plastic constitutive model. Using the results of three isotropically consolidated drained triaxial compression tests, a comparison between numerical and experimental results clearly shows the capability of the optimisation procedure to determine the model parameters correctly.     

Eutrophication of an Urban Forest Ecosystem: Causes and Effects

Doklady Earth Sciences - The combined use of methods of passive dosimetry of the status of atmospheric air, phytoindication, and cartographic visualization of data made it possible to elaborate and...     

Development and validation of an estuarine biotic integrity index

We tested hypotheses about how estuarine fish assemblages respond to habitat degradation and then integrated these responses into an overall index, the Estuarine Biotic Integrity Index (EBI), which summarized observed changes. Fish assemblages (based on trawl catches) and habitat quality were measured monthly or biweekly at nine sites in two estuaries from March 1988 to June 1990. Submerged aquatic vegetation habitats were classified as low or medium quality based on year-round measurements of chemical and physical characteristics (phytoplankton blooms; macroalgae; dissolved oxygen; nutrients; dredged channels). We tested 15 metrics and selected 8 for inclusion in the EBI: total number of species, dominance, fish abundance (number or biomass), number of nursery species, number of estuarine spawning species, number of resident species, proportion of benthic-associated fishes, and proportion abnormal or diseased. Fish assemblages in low-quality sites had lower number of species, density, biomass, and dominance compared with medium-quality sites. Fish abundance peaked in July and August, and was lowest in January to March. The seasonal cycle in low-quality sites was damped compared with medium-quality sites. Abundances of fishes using estuaries as a spawning and nursery area and of benthic species were lower in low-quality sites compared to medium-quality sites. The individual metrics and the overall index correlated with habitat degradation. The EBI based on biomass did not do better than the EBI based on number, indicating that the extra effort to obtain biomass may not be warranted. We suggest the EBI is a useful indicator of estuarine ecosystem status because it reflects the relationship between anthropogenic alterations in estuarine ecosystems and the status of higher trophic levels.     

The effect of nitrogen loading on a brackish estuarine faunal community: A stable isotope approach

Coastal ecosystems worldwide face increased nutrient enrichment from shoreline and watershed development and atmospheric pollution. We investigated the response of the faunal community of a small microtidal estuary dominated byRuppia maritima (widgeon grass) in Maine, United States, to increased nitrogen loading using an in situ mesocosm enrichment experiment. Community response was characterized by assessing quantitative shifts in macroinvertebrate community composition and identifying changes in food web structure using stable carbon and nitrogen isotope ratios of producers and consumers. The community was dominated by brackish water invertebrates including midge larvae, oligochaetes, damselfly larvae, amphipods, and ostracods. Experimental nutrient additions resulted in significantly lower densities of herbivorous chironomids and predatory damselflies and greater densities of deposit feeding oligochaetes. Grazing midge larvae (Chironomidae:Dicrotendipes, Cricotopus) consumed epiphytic algae under both natural and enriched conditions. Deposit feedingChironomus was dependent on allochthonous sources of detritus under natural conditions and exhibited a shift to autochthonous sources of detritus under enriched conditions. PredatoryEnallagma primarily consumed grazing chironomids under all but the highest loading conditions. Experimental nutrient loading resulted in an increase in generalist deposit feeders dependent on autochthonous sources of detritus.     

The Kolmogorov model of bed-thickness distribution: an assessment based on numerical simulation and field-data analysis

Kolmogorov's model of the distribution of bed thicknesses is assessed by numerical simulations of a sedimentation process, assumed to be a random time-series of alternating depositional and erosional episodes conformable with a stationary Markov process in a state of equilibrium. The study supports the validity of the main point of the model. The random time-series process generates a succession of beds with 'positive' (preserved) and 'negative' (eroded) thicknesses, the frequency distribution of which, f(x), spans the range of positive to negative x -values. The beds with negative thicknesses are absent in the stratigraphic record, whereby the measured bed thicknesses show a frequency distribution, f*( x | x > 0), that is left-side truncated, cut off at the zero thickness value. The numerical simulations further indicate that f( x ) is a 'composite' geometrical distribution, whose actual form changes progressively with p _d, the probability of sediment deposition relative to erosion. The distribution f( x ) invariably has a maximum at x ≤0, such that the truncated distribution f*( x ) for p _d≥0.5 is a simple geometrical distribution regardless of p _d value. The f*( x ) distribution will appear to be a negative exponential distribution when based on the bed-thickness data measured in a conventional metric scale. Data sets from four different turbidite successions in the Cenozoic of Japan, each comprising a few thousand beds, show this type of distribution. However, the sandstone-capping shales in one of the turbidite successions show a truncated Gaussian distribution, attributed to a significant component of non-turbiditic mud. No universal form of bed-thickness distribution can be assumed for the Kolmogorov model. The form of bed-thickness distribution may vary with the type of the depositional process and the character of the sedimentary environment.     

Silica in Lake Superior: mass balance considerations and a model for dynamic response to eutrophication

The dissolved silica concentration in waters of Lake Superior probably is in a steady state because it is not influenced significantly by man, and the climate, topography and vegetation in the drainage area of the lake have been stable for the past 4000 years. Therefore the rate at which dissolved silica is introduced to the lake should equal the output rate.The primary inputs are: tributaries (4.1–4.6 × 10⁸kgSiO₂/yr), diffusion from sediment pore waters (0.21?0.78 × 10⁸kgSiO₂/yr) and atmospheric loading (0.26 × 10⁸kgSiO₂/yr). Silica is lost from the lake waters by: outflow through the St. Marys River, diatom deposition, adsorption onto particulates in the sediments, and authigenic formation of new silicate minerals. Tributary outflow accounts for less than one half the annual input of silica, and diatom deposition and silica adsorption withdraw less than 10% of the annual input. Therefore the formation of new silicate phases must be the dominant sink for dissolved silica in Lake Superior. The specific phases formed are not identified in the bottom sediments. X-ray diffraction studies suggest that smectite is one product, and amorphous ferroaluminum silicates may be another product.Mathematical modeling of the dissolved silica response to lake eutrophication suggests that the phosphate loading to Lake Superior would have to increase by about 250-fold to cause a silica depletion rate equal to that reported for Lake Michigan, assuming no change in the rate of upwelling of deep waters.     

Loss on ignition and kjeldahl digestion for estimating organic carbon and total nitrogen in estuarine marsh soils: Calibration with dry combustion

Soils (n=250) were collected from ten salt and brackish-water marshes of North Carolina and analyzed for organic matter content by loss on ignition (LOI) and Kjeldahl nitrogen (KN). Total organic carbon and total nitrogen were determined on the same samples using an elemental CHN analyzer. Regression analyses indicated that LOI and KN were excellent estimators of organic C (R²=0.990) and total N(R²=0.986), respectively, in low clay content (0–11%) marsh soils containing a wide range of soil organic C (0.1–28%) and total N (0–1.6%). A quadratic equation best described the relationship between organic C and organic matter (Organic C=0.40 [LOI] +0.0025 [LOI]²) while a linear model accurately described the relationship between total N and Kjeldahl N (Total N=1.048 [KN]?0.010). The proportion of organic C in organic matter (C/OM) increased with increasing soil organic matter content, probably as a result of aging. Young marshes, which are characterized by low soil organic content contain C/OM ratios similar to emergent vegetation (40–45%). In old organic soils (70–80% organic matter), C/OM increased to 57–60% due to accumulation of reduced organic materials.     

Dynamic simulation of littoral zone habitats in lower Chesapeake Bay. I. Ecosystem characterization related to model development

The fringing environments of lower Chesapeake Bay include sandy shoals, seagrass meadows, intertidal mud flats, and marshes. A characterization of a fringing ecosystem was conducted to provide initialization and calibration data for the development of a simulation model. The model simulates primary production and material exchange in the littoral zone of lower Chesapeake Bay. Carbon (C) and nitrogen (N) properties of water and sediments from sand, seagrass, intertidal silt-mud, and intertidal marsh habitats of the Goodwin Islands (located within the Chesapeake Bay National Estuarine Research Reserve in Virginia, CBNERR-VA) were determined seasonally. Spatial and temporal differences in sediment microalgal biomass among the habitats were assessed along with annual variations in the distribution and abundance ofZostera marina L. andSpartina alterniflora Loisel. Phytoplankton biomass displayed some seasonality related to riverine discharge, but sediment microalgal biomass did not vary spatially or seasonally. Macrophytes in both subtidal and intertidal habitats exhibited seasonal biomass patterns that were consistent with other Atlantic estuarine ecosystems. Marsh sediment organic carbon and inorganic nitrogen differed significantly from that of the sand, seagrass, and silt habitats. The only biogeochemical variable that exhibited seasonality was low marsh NH₄ ⁺. The subtidal sediments were consistent temporally in their carbon and nitrogen content despite seasonal changes in seagrass abundance. Eelgrass has a comparatively low C:N ratio and is a potential N sink for the ecosystem. Changes in the composition or size of the vegetated habitats could have a dramatic influence over resource partitioning within the ecosystem. A spatial database (or geographic information system, GIS) of the Goodwin Islands site has been initiated to track long-term spatial habitat features and integrate model output and field data. This ecosystem characterization was conducted as part of efforts to link field data, geographic information, and the dynamic simulation of multiple habitats. The goal of these efforts is to examine ecological structure, function, and change in fringing environments of lower Chesapeake Bay.     

Suspension-feeding bivalves and the fate of primary production: An estuarine model applied to Chesapeake Bay

A probabilistic mathematical model of bivalve suspension-feeding in estuaries is based on bivalve abundance, filtering capacities, and water mixing parameters. We applied the model to five regions of the upper Chesapeake Bay, ranging from shallow tidal fresh habitats to deep mesohaline habitats, for the years 1985 to 1987. Model results indicated that existing suspension-feeding bivalves could consume more than 50% of annual primary production in shallow freshwater and oligohaline reaches of the upper Chesapeake Bay and Potomac River. In deep mesohaline portions of the Chesapeake Bay and Potomac River, suspension-feeding bivalves could consume only 10% of primary production. Independent estimates of benthic carbon demand based on benthic production supported the model predictions. Hydrodynamics of large estuaries restrict the potential of benthic suspension-feeders to crop phytoplankton production because the width and depth of these estuaries limit transport of pelagic waters to the littoral flanks of the estuaries where benthic suspension-feeders can be abundant. Benthic suspension-feeders are dominant consumers in shallow segments of the Chesapeake Bay system, but are suppressed in deeper segments. The suppression is below that set by hydrodynamic limits, and may be due to periodic hypoxia or other factors. Our results suggest that the proposed use of suspension-feeding bivalves to improve water quality of large estuaries will be limited by the depth and width of the estuary, unless the bivalves are suspended in the water column by artificial means.     

突变模型势函数的一般表示式及用于富营养化评价

通常的初等突变评价模型仅给出控制变量维数n≤4的突变模型的势函数及相应的归一化公式,对高维(n≥5)的复杂系统需将其分解为若干维数小于4的多层子系统后再递归进行,且一般只给出各评价结果的相对排序.通过对初等突变模型势函数形式和相应的归一化公式的观察、比较和分析归纳,推演出包括任意维的突变模型的势函数形式及其相应的归一化公式.将推导出的突变评价归一化公式和分层递阶降维突变评价模型相结合,实现对指标众多的复杂系统的评价和分类.将突变评价公式应用于北京市21个湖泊的富营养化评价,并与多种评价方法进行了比较.结果表明,除1个湖泊的评价结果有相邻一级之差外,其余20个湖泊的评价结果完全一致,表明推演出的高维突变势函数形式和归一化公式是合理的.将其用于湖泊富营养化评价具有简单、实用的特点.     

Absence of overall feedback in a benthic estuarine community: A system potentially buffered from impacts of biological invasions

Species introductions are among the most dramatic human-induced impacts on aquatic and terrestrial ecosystems around the world. Stability patterns of an estuarine benthic community were investigated through guild interaction models representing the community before and after human-mediated species invasions. The study area was Yaquina Bay, a developed estuary on the central Oregon coast, U.S., where at least 12 species of nonindigenous invertebrates have been inadvertently introduced. Three of the introduced species (the polychaetes Hobsonia florida and Pseudopolydora kempi and the cumacean Nippoleucon hinumensis) are probably among the 10 most abundant invertebrate species in the intertidal benthic community. To estimate effects and potential risks of species introductions on the native community we constructed 2 types of community models based on functional-group interactions, namely, activity guild models and trophic guild models. In both cases we observed that overall feedback has a strong tendency towards zero in pre-invasion and post-invasion models. We generated 12,000 random models of similar size and could not detect this tendency. We suggest that the weak or absent overall feedback in this community may be an ecological property and not an intrinsic property of large systems as such. The reduced response to input from either invertebrate invasions or removal of native top predators, may to some extent buffer the community from such impacts. Alternative guild models suggested increased risk of stability decline in the invaded community even after accounting for potential complexity effects on stabllity. Further species introductions in this intermediately invaded estuary should be avoided.     

Ethane- and propane-producing potential and molecular characterization of an ethanogenic enrichment in an anoxic estuarine sediment

Ethane and propane are low molecular weight hydrocarbons observed widely at trace levels in cold marine sediments where thermogenic sources are considered insignificant, but their biological sources remain poorly constrained. In this study, several C₂ and C₃ compounds including alkenes, alcohols, thiols and carboxylic acids with a C₂ or C₃ skeleton were tested for their relative alkane-producing potential in an anoxic estuary sediment. Maximum conversion efficiency of substrates to ethane or propane was observed in the sediment supplemented with ethylene (up to 38%), followed by additions with ethanethiol (0.01%) and propanethiol (0.003%). Experiments with sterilized sediment, 2-bromoethanesulfonic acid or NaNO₃ were negative for alkane production, suggesting that methanogens were involved in alkane generation. Detailed investigation on ethanogenesis from ethylene showed that this reaction required H₂ but at reasonably low concentration (< 120 nmol dissolved H₂ l⁻¹ slurry) and caused a slight stable carbon isotope effect (ε_{ethane/ethylene} = −8.6 ± 2.4‰). The high ethane-producing potential, reasonable H₂ requirement and extensive occurrence of ethylene make ethylene reduction a plausible explanation for ethane in cold marine sediment. Phylogenetic analysis was first carried out with an ethane-producing enrichment with ethylene as the substrate and showed a dominance of homoacetogenic bacteria and the methanogenic genus Methanocalculus. Although we cannot rule out the possibility that other methanogens in the gene libraries are responsible for ethanogenesis from ethylene, the dominance of Methanocalculus, with its hydrogenotrophic cultured representatives, is in accord with our biogeochemical observation that H₂ is required for this reaction.     

The characterization of axenic culture systems suitable for plant propagation and experimental studies of the submersed aquatic angiospermPotamogeton pectinatus (Sago Pondweed)

Clonal lines of the submersed aquatic angiospermPotamogeton pectinatus were grown in three culture systems. The first, which used sucrose as a carbon source in a liquid medium, supported vigorous vegetative growth and can be used to propagate large numbers of plants in axenic conditions. In this culture system, plants were responsive to increasings photosynthetically active radiation (PAR) photon flux density (PFD) and were photosynthetically competent. However, their growth was heterotrophic and root development was poor. When these plants were transferred to a second nonaxenic culture system, which used 16-1 buckets containing artificial sediments and tap water, growth was autotrophic and plants were morphologically identical to field-harvestedP. pectinatus. The last culture system which consisted of a sand substrate and inorganic nutrient bathing solution aerated with 135 ml min^?1 ambient air enhanced to 3.0% CO₂ was axenic and supported autotrophic growth by plants that were also morphologically normal.